Phagocytosis and resorption during the reassembly of dissociated embryonic cells of sea urchins.

Time-lapse and electron microscopic observations were made on both epithelial and mesenchymal cells during the reassembly of embryos from dissociated cells of Strongylocentrotus purpuratus. In epithelial cells, where lysosomes are produced through the fusion of saccules formed from Golgi bodies, both phagocytosis of cell debris and resorption of differentiated cell structures were observed. In these cells, the lysosomes migrate and fuse with both autosomes and phagosomes. On the other hand, in the mesenchyme cells, where lysosomes are produced through the direct enlargement of the Golgi body's cisterna, neither phagocytosis nor resorption was observed. The migration of the lysosomes to the epithelial cell margins is the first indication of a re-establishment of cellular polarity after dissociation.